1. Field of the Invention
The invention relates to an analysis element for the determination of an analyte in a liquid sample, said analysis element having a carrier layer which contains, in a reagent domain, a reagent applied in a defined pattern by an ink-jet process.
2. Description of the Prior Art
Analytical examinations on liquid samples, especially body fluids such as blood or urine, are frequently carried out with the aid of analysis elements, which are also referred to as: solid state analysis elements. They are available in a variety of external forms, especially as extended test strips and as small square sheets. In every case, they have one or more test layers which contain the reagents required for the analysis. The test layers are brought into contact with the liquid sample and the reaction of the analyte with the reagents produces a physically measurable detection signal, especially a colour change which can be measured visually or photometrically. Examples of other known detection signals are optical fluorescence, luminescence and, in the case of electrochemical analysis elements, voltage or current signals.
Particular importance has recently been attached to analysis elements which work on the basis of a specific binding reaction between two bioreactive binding partners. Specific binding reactions in this sense are especially immunological interactions, i.e. interactions between antigens or haptens on the one hand and antibodies on the other. However, it is also possible to use other specific bioreactive interactions such as lectin-sugar, an interaction between an active substance and a receptor, the specific binding between biotin and streptavidin or certain enzyme-substrate binding reactions, e.g. inhibitors or suicide substrates.
The reagents are generally incorporated in the test layers, the normal case being either that a porous support matrix (e.g. made of paper or plastic) is impregnated with reagent or that, in a layering process, a reagent film is produced which contains the reagents dissolved or dispersed in a film former. As a rule, in the manufacture of analysis elements, different mutually incompatible reagents have to be accommodated so as to be spatially separated. This is conventionally achieved by joining together (e.g. by welding or adhesive bonding) individual preprepared reagent support elements. These processes are very expensive, often cause production defects and only allow limited miniaturization.
It has recently been proposed to use the ink-jet technology originally developed for computer printers (ink-jet printers) in the manufacture of analysis elements. In this context, reference may be made to EP-A-119573 and EP-A-268237 (U.S. Pat. No. 4,877,745). Both patent specifications contain more detailed explanations of the previously known state of the art, including ink-jet technology in particular, to which reference is made here.
The distinguishing feature of the ink-jet technique is that very small quanta (partial amounts) of a liquid can be applied as drops to a carrier layer with high precision, the precision relating both to the exact positioning of the dot produced by the drop of reagent on the reagent domain and to the reagent volume. The drops can be ejected successively at high frequency.
Reagent patterns produced by an ink-jet process differ unambiguously from the patterns obtainable by other printing techniques. In particular, comparably fine reagent dots cannot be produced in any other way with similar uniformity.
A special variant of the ink-jet technique, which is also particularly suitable for the invention, is the drop-on-demand technique, where individual drops of liquid can be produced at any desired point in time and applied to a carrier layer. In connection with the metering of biochemical analytical liquids, especially reagents, only the technique described in the mentioned patent specifications has so far been used, where the volume of a jet chamber is compressed every time a drop is to be ejected. A piezoelectric change in the volume of the jet chamber is utilized in particular here. In U.S. patent application entitled "Method and device for the metered application of a biochemical analytical liquid to a target" U.S. patent application Ser. No. 07/735,580 filed of even date herewith by the present invention now abandoned, the use of bubble-jet technology for the application of liquid reagents to a reagent domain is described which is also suitable for the present invention, and such copending application is hereby incorporated by reference. The term ink-jet is to be understood hereafter as encompassing both said procedures.
The ink-jet technique makes it possible to apply reagents to a reagent domain of an analysis element, with high precision and uniformity, as a reagent layer of exceptionally low thickness. Said patent specifications also mention the possibility of applying the reagent to the carrier layer in a particular pattern, e.g. in order to allow a direct comparison between a subdomain coated with reagent and a reagent-free subdomain, or in order to make the result of the analysis more clearly visible, because the formation of colour appears for example in the form of a plus or minus sign.
De-A-27 27 347 and De-C-27 29 233 have disclosed an alternating arrangement of dots (especially spots) of different reagents which are applied by a screen printing technique. However, this process is very expensive. Moreover, the amounts of reagent applied cannot be metered accurately. The dots are relatively large and can only be miniaturized to a limited extent. Many reagents cannot be processed to pastes suitable for screen printing without being damaged or having their properties changed, so this process, which has been know for a long time, has not achieved any practical significance.